[sdiy] Group Level Shift?

[Michael Ruberto]

HI

>
>First, you will need 6 op-amps - used in pairs - one inverting buffer
>followed by a scond to re-invert.

Yes this is what I had in mind.

>
>Consider this - What is the voltage at the inverting input of the standard
>op-amp inverting buffer. It is 0V - the "virtual ground" or summing node.
>
>It will be 0V at the summing nodes of the three input buffers.
>
>If all three are tied together through resistors as per your suggestion, 
>how
>much interaction will there be, considering all of their other ends of 
>these
>resistors are at 0V. None. In the real world there will be a little
>interaction related to slew rates, but so slight it can be ignored.

So if I was actually worried about this I might be looking to use something 
with a 15V slew like the LF353. But since this is simply going to shift the 
outputs of my LFO I guess I'll just use another cheap LM324. I don't need 
any precision here at all really, just want to be sure all signals are 
centered properly to avoid overlap.
This is great, I soooo didn't want to pay $18 for a dang 3PDT switch!!

Thanks  Ken!!

M. A. Ruberto

>
> >I have 3 separate signals that I want to level shift at the same time 
>from
> >one switch. The signals are all +/-5. I want to have a toggle switch that
> >will shift the signals to 0 > +10, -5 > +5, and 0 > -10. Of course I want 
>to
> >do it as economically as possible. Can I do it by simply adding a bias
> >resistor to the inverting input of an op-amp, plus the signal, and using 
>a
> >switch to connect that resistor to either - rail, + rail or nothing?
> >keep in mind there would be 3 op-amps - 1 per signal. If I connect the 
>bias
> >resistors to the center of a SPDT switch will I get bad interactions 
>between
> >the 3 channels when the switch is in the "off" position? Should I be 
>looking
> >at a 3PDT for this?
> >Does this even make sense?
> >
> >Thanks
> >
> >M. A. Ruberto
> >
> >
> >
>_______________________________________________________________________
>Ken Stone   sasami at hotkey.net.au or sasami at cgs.synth.net
>Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
>Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>
>